Deflection compensating press brake die support

ABSTRACT

Apparatus for eliminating faulty bends in press brakes due to deflection between the ram and bed of a press brake which is greatest at the mid point. A compressible polyurethane member is interposed between the die and bed of the press brake and is of such thickness that it compresses to a degree approximately one order of magnitude greater than the total deflection of the bed and ram at the mid point. The polyurethane member is of substantially the same length and in registry with the bend line of the workpiece. Means are also provided for readily lifting the die member to provide polyurethane inserts of a total length to match the bend line of the workpiece.

United States Patent Swenson et al.

[54] DEFLECTION COMPENSATING PRESS BRAKE DIE SUPPORT [72] Inventors:Donald G. Swenson, Eggertsville; George H. Trautman, Jr., Kenmore,

both of NY.

[73] Assignee: Niagara Machine 8: Tool 'Works,

, Buffalo, NY.

[22] Filed: Sept. 9,1971

[21] Appl. N0.: 178,892.

3,561,241 2/1971 Blain ..72/465 Primary Examiner-Lowell A. A ttomey-Conrad Christel, et; a1.

[ ABSTRACT Apparatus for eliminating faulty bends in press brakes due todeflection between the ram and bed of a press brake which is greatest atthe mid point. A compressible polyurethane member is interposed betweenthe die and bed of the press brake and is of such thickness that itcompresses to a degree approximately one order of magnitude greater thanthe total deflection of the bed and ram at the mid point. Thepolyurethane member is of substantially the same length and in registrywith the bend line of the workpiece. Means are also provided for readilylifting the die member to provide polyurethane inserts of a total lengthto match the bend line of the workpiece.

16 Claims, 3 Drawing Figures PArENTEgmumz 3,702,558

.smzzuorz x mm F16. DONALDYG. SWENS:

I I H.TRA

GEORGE INVENTORS v UTMAN,

ATTORNEYS DEFLECTION COMPENSATING PRESS BRAKE DIE SUPPORT BACKGROUND OFTHE INVENTION This invention relates to press brake die supporting meansand particularly to novel supporting means which substantiallyneutralizes the deflection of the punch and die members and thus avoidsthe production of malformed bends due to deflection of the bed and ramof the press brake.

When a press brake punch and die engage a metal sheet to effect a bendtherein, the die and its supporting structure and the punch and the ramto which it is secured all deflect, the ram deflecting upwardly and thebed deflecting downwardly, and since the greatest deflection is at themid-points of the punch and die, the punch does not enter the die to asgreat a degree at the mid-point as at the ends of the punch and die.This results in a bend which is of greater included angle at themid-point of the workpiece than at the ends and produces a bowed orwarped workpiece.

Various expedients have been employed in attempts to avoid theobjectionable bend formations resulting from the deflection of pressbrake dies and punches. For instance, some press brake manufacturersbuild camber into the press bed to compensate for deflection. Thisexpedient obviously can correct for only one set of conditions whereasthere are numerous variables such as the thickness of the workpiece, thelength of the bend line, the angle of the bend, the kind of material,etc.

Another expedient is to shim the die holder to introduce camber tocounteract deflection. This is a tedious, makeshift procedure and, to beeffective, would require re-shimming with changes in any of the abovevariable conditions.

' SUMMARY OF THE INVENTION The present invention provides a convenientand practical arrangement for neutralizing the deflection of the punchand die members and their supporting parts.

In bending metal sheets in a press brake the tonnage per linear inch ofbend line is constant over the length of the bend line excepting at thevery ends wherelateral contraction of the sheet is unresisted and thetonnage drops off somewhat. This latter effect is of littlesignificance. When the mid portions of the bed and ram of the pressbrake deflect and the punch accordingly does not enter the die as far asat the ends, the tonnage per linear inch at such mid-points will be lessthan at the ends of the worksheet. Any die arrangement that insuresuniform unit pressure against the workpiece along the entire bend linewill produce good bends of constant angle throughout, regardless of theamount of deflection of the bed and ram at their midpoints.

The present invention provides a very close approach to such uniformpressure per inch of bend line along the entire length of the bend byintroducing an elastic medium of uniform spring constant per linear inchof die holder, such elastic medium being inserted under the die holderfor the length of the workpiece to be bent, that is, between the dieholder and the bed of the press brake. This elastic medium may be eithercontinuous or of closely spaced units. The same theoretical results areattained if the elastic medium is interposed between the ram and thepunch carried thereby and in fact the elastic medium may be providedbetween both the punch and ram and between the die and bed.

To achieve the desired results of the present invention, the totalvertical deformation of the elastic medium must be a number of timesgreater than the degree of deflection of the bed and ram of the machineunder a given load. The total vertical deformation of the elastic mediumshould be preferably at least about one order of magnitude greater thanthe deflection and if a greater order of magnitude is provided, betterbends will be produced.

While various materials and dimensions may be employed, successfuloperation has been achieved by using polyurethane of durometer hardness.A piece two inches square in transverse section and of a length equal tothe length of the workpiece along the bend line was interposed betweenthe press brake die and the bed of the press. This produced excellentbend results with standard punch and die units.

By way of explanation, if a given load employing the elastic medium ofthe present invention would normally produce a total deflection of bedand ram of 0.015 inches, which deflection would be of a degree whichwould produce unsatisfactory bends, and if such load produced a totalapproximate vertical compression of the elastic medium of say 0.150inches at the center of the bend, then the compression of the elasticmedium at the ends of the bend would be 0.165 inches. The elastic mediumwould then exert a pressure at the center of the bend equal to about 90per cent of the pressure at the ends of the bend line.

This degree of upward pressure exerted against the center of the die bythe elastic medium arches the die upwardly at the center toward thepunch to a degree which closely matches the upward arch of the punch dueto deflection, and thus produces excellent bends. It is to be understoodthat the more or less matched arching of the punch and die in forming abend is immaterial as far as curving the workpiece is concerned sincethis degree of arching is far within the elastic limit of materialswhich would usually be formed in this manner.

An important feature of the present invention is that the length of theelastic medium acting between the die and bed (or the punch and ram, asthe case may be) be of the same length and in vertical registry with thelength of the bend in the workpiece. If the elastic medium issubstantially longer than the bend line, then the projection of theelastic medium beyond the bend line will arch the portion of the diebeyond the bend line and this arching will affect the arching of the diealong the bend line to a degree which defeats the purposes of thepresent invention. Similarly, if the elastic medium is substantiallyshorter than the bend line, then the die would tend to arch reverselybeyond the ends of the elastic medium outwardly to the ends of the bendline, again producing an entirely unsatisfactory result.

With the elastic medium of substantially the same length and in registrywith the bend line, the portions of the die projecting beyond the bendline will be under no bending stress and will merely project outwardlyin a straight line tangent to the arched portion of the die at the endsof the elastic medium. Thus the inactive portions of the die beyond thebend line do not aggravate the deflection condition within the bend linewhich they would do if the polyurethane were present between the die andbed beyond the ends of the bend line to cause deflection of the diebeyond such ends.

BRIEF DESCRIPTION OF THE DRAWINGS paratus shown in FIG. I viewed fromthe front of the press brake and showing the die parts in position foroperation; and

FIG. 3 is a similar view showing the die element in a raised positionfor changing polyurethane inserts.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT In FIG. 1 the numeraldesignates the lower portion of the ram of a press brake and the numeral11 shows the upper die supporting portion of the bed of such pressbrake. In the present instance, the ram 10 has attached thereto aconventional punch 12 which is attached to the ram by a horizontal clampbar 13. All of this construction is entirely conventional.

In FIG. 1 a die member for cooperation with punch 12 is designated 14and the manner in which die 14 is supported on bed 1 1 is as follows. Apair of die supporting rails are indicated at 15 and 16, rail 15comprising a base for the die support and rail 16 comprising a topplate. The facing surfaces of rails 15 and 16 are longitudinallyrecessed as shown in FIG. 1 to receive a longitudinally extending bar 17of a compressible medium which, by way of example, may comprisepolyurethane. In actual practice polyurethane having a durometerhardness of 90 has been found satisfactory for operating under averageloading conditions. Again merely by way of example, the bar 17 may betwo inches square in transverse section.

As indicated earlier herein it is essential that the length of thecompressible medium, in this case bar 17, be substantially the samelength as the bend line in the workpiece so that it registers verticallytherewith. Specifically, the purposes of the present invention aredefeated if bar 17 is of substantially greater length than the bend linein the workpiece so that it supports the die member beyond the workpieceat one or both ends of the bend line. Similarly, the purposes of thepresent invention will not be attained if the bar 17 is substantiallyshorter than the bend line. For this reason, it is necessary in thepresent example to adjust the length of the compressible medium 17whenever a workpiece having a different length of bend line is to beformed in the press brake.

It is to be understood that the compressible medium 17 may be made up ofany number of pieces of polyurethane in end-to-end relationship betweenthe die rails 15 and 16. To facilitate adding or subtracting from thelength of the polyurethane member 17 to suit the length of the bend tobe formed, means are provided for conveniently lifting top plate 16 ofthe die rail structure and the die 14 which is carried thereon, leavingthe polyurethane compressible member 17 fully exposed for convenientreplacement or for additions or removals of portions of the member 17.

The means for thus lifting top plate 16 and die 14 is illustrated inFIGS. 2 and 3 which show the right-hand end of the die structure, viewedat right angles to FIG. 1, but it is to be understood that duplicatelifting mechanism of opposite hand will be provided at the left-hand endof the die structure.

A mounting plate 20 is fixed to each end of base 15 of the die railstructure and has fixed thereto a mounting bracket 21. A pair of plates22 are fixed to opposite sides of a handle member 23 asby rivets 24 andplates 22 are pivotally connected to hearing portions 25 of bracket 21.A lifting rod is designated 26 in FIGS. 2 and 3 and a link 27 is pivotedto the lower end of rod 26 as at 28 and to an intermediate point onplates 22 as at 29.

Rod 26 is mounted for vertical sliding movement in a bushing 32 carriedby bearing formations 33 on bracket 21 and rod 26 is fixed adjacent toits upper end to a bracket 35 which is secured to the end of upper plate16 of the die rail structure. For adjustably attaching the upper end ofrod 26 to bracket 35, a stud 36 is threaded into the upper end of rod 26and is attached to bracket 35 by a pair of lock nuts 38 which provideaxial adjustment of rod 26 relative to bracket 35.

In the position shown in FIG. 2, handle 23 is in a lowered position sothat upper plate 16 and die 14 are resting freely on the polyurethanemember 17 and the latter may readily compress under vertical loadsagainst the die member upon which the handle members 23 will swingfreely toward the ends of bed 11. When polyurethane member or members 17are to be replaced, added to, or subtracted from, the handles 23 atopposite ends of the die structure are raised to the positionillustrated in FIG. 3. The parts will normally remain in this positionunder the force of gravity by reason of the fact that during thisraising movement of handle 23, pivot 29 moves over center with respectto the pivotal connection of plates 22 with bearing formations 25 andthis over-center movement is limited by abutment between portions ofhandle member 23 and link 27, as clearly shown in FIG. 3.

After proper length adjustment of the compressible medium 17 isaccomplished to match such length to the length of the line of bend inthe workpiece, handles 23 are manually lowered to the position shown inFIG. 2 and the parts reassume the position shown in FIG. 1.

The foregoing provides a very practical and workable arrangement tocompensate for the deflection of the bed and ram of a press brake. Amore elaborate arrangement which fully compensates for this deflectionis to introduce a closely and uniformly spaced row of hydrauliccylinders between the die and bed, or between the punch and ram. Thesecylinders are interconnected to exert uniform pressures and means areprovided so that only the cylinders within the limits of the length ofthe bend line are operative, the remaining cylinders being bypassed orotherwise cut out of the system.

A preferred embodiment has been described herein and shown in theaccompanying drawings to illustrate the underlying principles of theinvention but it is to be understood that numerous modifications may bemade without departing from the broad spirit and scope of the invention.

We claim:

1. In a press brake having a bed, a ram movable toward and away fromsaid bed, a die mounted on said bed, and a punch carried by said ram,compressible means extending linearly between said die and the bed ofthe press brake and having a substantially uniform spring constant perinch along said die and having a vertical deformation under a given loadapproximately one order of magnitude greater than the combined maximumdeflection of the bed and ram of the press brake under such given loador greater.

2. A press brake according to claim 1 wherein said compressible meansextends substantially the same length as the bend line of the workpiece.

3. A press brake according to claim 2 wherein said compressible meanscomprises a body of polyurethane.

4. A press brake according to claim 3 wherein said polyurethane has ahardness of approximately 90 durometer.

5. Apparatus according to claim 2 having means at opposite ends of saidbed engageable with said die for elevating the same to facilitateadjusting the efiective length of said compressible means to match thelength of said bend line.

6. Apparatus according to claim 2 having means at opposite ends of saidbed engageable between said bed and said die for raising the latter andmaintaining the same temporarily in raised position to permit adjustmentof the effective length of said compressible means to match the lengthof said bend line.

7. A press brake according to claim 1 wherein said compressible meanscomprises a body of polyurethane.

8. A press brake according to claim 7 wherein said polyurethane has ahardness of approximately 90 durometer.

9. Apparatus according to claim 7 having means at opposite ends of saidbed engageable with said die for elevating the same to adjust the lengthof the polyurethane body to match the length of said bend line.

10. Apparatus according to claim 7 having means at opposite ends of saidbed engageable between said bed and said die for raising the latter andmaintaining the same temporarily in raised position to permit adjustmentof the length of said polyurethane body to match the length of said bendline.

11. In a press brake having a bed and a ram, a die member carried bysaid bed and a punch member carried by said ram, and compressible meansinterposed between at least one of said members and its respectivecarrier and extending linearly along said member, said compressiblemeans having a substantially uniform spring constant along said memberand having a total vertical deformation under a given load approximatelyone order of magnitude greater than the combined maximum deflection ofthe bed and ram of the press brake under such given load or greater.

12. A press brake according to claim 11 wherein said compressible meansextends substantially the same length as the bend line of the workpiece.

13. A press brake according to claim 12 wherein said compressible meanscomprises a body of polyurethane.

14. A press brake according to claim 13 wherein said polyurethane has ahardness of approximately durometer.

15. A press brake according to claim 11 wherein said com r ssible meanscom rises' 01 rethane.

16? 1 press brake accoi ding 3) claim 15 wherein said polyurethane has ahardness of approximately 90 durometer.

1. In a press brake having a bed, a ram movable toward and away fromsaid bed, a die mounted on said bed, and a punch carried by said ram,compressible means extending linearly between said die and the bed ofthe press brake and having a substantially uniform spring constant perinch along said die and having a vertical deformation under a given loadapproximately one order of magnitude greater than the combined maximumdeflection of the bed and ram of the press brake under such given loador greater.
 2. A press brake according to claim 1 wherein saidcompressible means extends substantially the same length as the bendline of the workpiece.
 3. A press brake according to claim 2 whereinsaid compressible means comprises a body of polyurethane.
 4. A pressbrake according to claim 3 wherein said polyurethane has a hardness ofapproximately 90 durometer.
 5. Apparatus according to claim 2 havingmeans at opposite ends of said bed engageable with said die forelevating the same to facilitate adjusting the effective length of saidcompressible means to match the length of said bend line.
 6. Apparatusaccording to claim 2 having means at opposite ends of said bedengageable between said bed and said die for raising the latter andmaintaining the same temporarily in raised position to permit adjustmentof the effective length of said compressible means to match the lengthof said bend line.
 7. A press brake according to claim 1 wherein saidcompressible means comprises a body of polyurethane.
 8. A press brakeaccording to claim 7 wherein said polyurethane has a hardness ofapproximately 90 durometer.
 9. Apparatus according to claim 7 havingmeans at opposite ends of said bed engageable with said die forelevating the same to adjust the length of the polyurethane body tomatch the length of said bend line.
 10. Apparatus according to claim 7having means at opposite ends of said bed engageable between said bedand said die for raising the latter and maintaining the same temporarilyin raised position to permit adjustment of the length of saidpolyurethane body to match the length of said bend line.
 11. In a pressbrake having a bed and a ram, a die member carried by said bed and apunch member carried by said ram, and compressible means interposedbetween at least one of said members and its respective carrier andextending linearly along said member, said compressible means having asubstantially uniform spring constant along said member and having atotal vertical deformation under a given load approximately one order ofmagnitude greater than the combined maximum deflection of the bed andram of the press brake under such given load or greater.
 12. A pressbrake according to claim 11 wherein said compressible means extendssubstantially the same length as the bend line of the workpiece.
 13. Apress brake according to claim 12 wherein said compressible meanscomprises a body of polyurethane.
 14. A press brake according to claim13 wherein said polyurethane has a hardness of approximately 90durometer.
 15. A press brake according to claim 11 wherein saidcompressible means comprises polyurethane.
 16. A press brake accordingto claim 15 wherein said polyurethane has a hardness of approximately 90durometer.